Hypersensitivity Reactions

Abstract

Egyptian hieroglyphics describe the sudden death of a pharaoh following a wasp sting in 2640 BC, possibly the first recorded account of an anaphylactic reaction (1,2). Anaphylaxis is the most extreme, life-threatening systemic manifestation of a hypersensitivity reaction that occurs in a sensitized host who is re-exposed to an inciting antigen. The yearly incidence of anaphylactic reactions in the general population is about 1 per 2.5 million people (3). In the hospitalized population, where exposure to allergenic substances is more common, the incidence may be as high as 1 per 1,700 patients (4). Other less severe forms of hypersensitivity reactions occur with even greater frequency. Accordingly, familiarity with hypersensitivity reactions, especially anaphylaxis, is extremely important in caring for critically ill patients.